PROJECT SUMMARY- ?7 nicotinic receptors are widely distributed throughout the human brain, and are enriched in regions required for cognition, sensory processing, attention, working memory and reward. They have been implicated in neurodegenerative diseases such as Alzheimer?s and Parkinson?s and psychiatric diseases such as schizophrenia, and disorders of attention and cognition. ?7 receptors are also present in non-neuronal cells where they contribute to a variety of anti-inflammatory pathways. The overall goal of the proposed research is to develop a mechanistic understanding of activation and modulation of ?7 receptors applicable to therapeutic drug design. This proposal will investigate how calcium potentiates ?7 nicotinic receptors activated by the low agonist concentrations that prevail physiologically. We have developed a co- agonist hypothesis that not only can explain how ?7 signals despite being far from cholinergic nerve terminals, but it also suggests calcium fluctuations associated with neuronal firing regulate ?7 signaling. To investigate calcium potentiation of ?7, X-ray crystallographic methods will be used to determine atomic resolution structures of an ?7 ligand binding domain bound with the potentiating ions calcium and barium. In parallel, single molecule electrophysiological methods will define the kinetic mechanism behind divalent ion potentiation. Finally, application of molecular biological and single molecule electrophysiological methods will identify amino acid residues in ?7 that mediate divalent cation potentiation, and determine the stoichiometry with which divalent cations potentiate. Completion of this project will reveal mechanistic underpinnings of activation and calcium regulation of ?7 applicable to neurological disease treatment and therapeutic drug design.